Solid-state lighting is an attractive alternative to incandescent and fluorescent lighting systems for a wide range of lighting applications, and in particular for exterior applications, because of its relatively higher robustness, and long life. However, conventional solid-state lighting systems featuring light-emitting diodes (LEDs) have a number of limitations related to thermal management of heat generated by the LEDs that may complicate the fabrication of sealed, weatherproof or waterproof systems. Because of the sealing requirements, traditional exterior LED lighting systems typically have a rigid structure and a fixed size, making it difficult to illuminate arbitrarily sized areas. For example, back lighting, either for decorative or signage purposes, is widely used in exterior applications, and in most cases, the size and shape of the area to be illuminated is not a perfect fit for traditional exterior lighting systems. Such backlighting systems may have very large sizes, for example hundreds of feet on a side, may have odd shapes, such as curve or non-right-angle joints or may not be flat, but have a three-dimensional shape. The result is uneven illumination, for example relatively darker regions in between each illumination unit and at the edges of the area, which cannot effectively be illuminated by fixed size systems or relatively brighter areas associated with each illumination unit in the system.
Traditionally the issue of uneven illumination is addressed by increasing the depth of the lighting system and/or reducing the transmittance of the surface to be illuminated. While both of these approaches do address the issue of uneven illumination, these solutions come with increased cost, reduced efficiency and undesirable aesthetics.
In many lighting applications it is desirable to have lighting systems or luminaires that are thin, low-volume, and lightweight in order to meet certain building requirements, aesthetic design requirements or so that the lighting system is unobtrusive. In other applications it is desirable to be able to conform the illumination source to a curved surface. Increasing the depth of the system to achieve acceptable intensity uniformity is at odds with these needs and also increases the cost of the system because more material is required for the system itself as well as the mounting hardware. Reducing the transmittance of the illuminated surface also reduces the system efficiency.
In both cases, the actual flux from the LEDs typically must be increased to achieve the desired intensity of the illuminated surface, increasing the up-front and operating costs, as well as adding more cost and complexity for thermal management of the heat generated by the additional LEDs. In large measure the heat from LEDs is generally extracted by conduction, which typically requires relatively large amounts of material with a high thermal conductivity, such as metal core printed circuit boards (MCPCBs), heat sinks, and in some cases active (e.g., forced-air) cooling. Such thermal-management solutions are significantly more complicated when required to be located within a sealed system and are typically not sufficiently flexible to permit conforming to curved surfaces. Furthermore, they take up significantly more space than the LEDs themselves, resulting in increased size and volume of exterior LED-based lighting systems. In addition to higher cost, exterior LED lighting systems may have potentially reduced reliability and operational lifetime resulting from higher LED junction temperatures that may exist in sealed systems.
In view of the foregoing, a need exists for systems and techniques enabling the low-cost design and manufacture of sealed and sealable compact, reliable, high-brightness lighting systems able to produce uniform illumination over arbitrarily sized areas.